The vision of a network based defence demands that its C4I-system, FMLS, shall co-operate with external systems, e.g. civilian systems or systems from other nations. When subsystems are connected a lot of security issues arise. One is authentication, i. e. verification of identities stated by different parties, across system borders. Parties to authenticate include not only humans, but also digital objects like computers, mobile software code, radio sets etc. The main part of the report describes Web Services and developing standards for authentication within Web Services. Since this area is developing, the report is descriptive rather than assessing. One conclusion is that authentication of a human user to a Web Service is under way, but authentication between Web Services is in its infancy.